1. Field of the Invention
The invention relates to a damper mechanism, and particularly a damper mechanism having coil springs having an irregular pitch.
2. Background Information
A damper mechanism used in a clutch disk assembly of a vehicle is formed of an input rotary member, an output rotary member, and an elastic coupling. The input rotary member can be coupled to an input flywheel. The output rotary member is preferably coupled to a shaft of a transmission. The elastic coupling mechanism elastically couples the input and output rotary members in a rotating direction. The input rotary member is formed of a clutch disk and a pair of input plates fixed to the clutch disk. The output rotary member is formed of a hub, which is unrotatably coupled to the transmission shaft. The hub is formed of a cylindrical boss spline-engaged with the transmission shaft and a radial flange formed around the boss. The elastic coupling mechanism is formed of a plurality of coil springs. Each coil spring is arranged in a window aperture formed in the flange, and is supported in windows formed in the input plate pair. The damper function described above absorbs and damps torsional vibrations applied to the clutch disk assembly.
The coil spring may have an irregular-pitch structure, in which spaces between coil wire portions are not constant. In this structure, the number of active turns changes and the spring constant changes when a portion of coils abut against each other. Thus, the single coil spring can exhibit multiple stages in torsion characteristics. More specifically, a portion or portions of the coil spring abut against each other after a region of low rigidity is ensured so that a predetermined stop torque may be obtained by increasing the spring constant.
When the coil spring is compressed in the disk rotating direction, the radially outer portion is compressed to a larger extent than the radially inner portion. This is due to the fact that a radially outer portion, e.g., of an edge of a window, which pushes the coil spring, moves a longer distance in the rotating direction than its radially inner portion. Therefore, the coil spring having an irregular pitch must be configured to have a wire-space (i.e., a large space between neighboring wire portions) in the radially outer portion, which is larger than that in the radially inner portion, for simultaneously bringing the radially outer and inner portions into the intimate contact states (i.e., fully compressed states).
However, during the operation of the damper, the coil spring may rotate around its own axis within the window. If rotated, the positions of the end portions of the coil spring change so that the portion of a smaller wire-space may move to a radially outer side, moving the portion of a large wire-space to a radially inner side. If moved, the coil spring is compressed in a manner such that the radially outer portion is fully compressed excessively quickly, and full compression of the radially inner portion is delayed or does not occur. More generally, the rotation of the coil spring may change the change timing of the torsion characteristics (timing of the change in the spring constant due to spring compression) as well as the torsional rigidity so that the intended torsion characteristics cannot be obtained.
In view of the above, there exists a need for damper mechanism which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the present invention is to achieve intended torsion characteristics in the damper mechanism using coil springs with an irregular pitch.
According to a first aspect, a damper mechanism includes an input rotary member, an output rotary member, and a coil spring assembly. The coil spring assembly is employed for elastically coupling the input and output rotary members in a rotating direction. The coil spring assembly includes an irregular pitch coil spring and a pair of spring seats. Each spring seat is engaged with an end of the coil spring such that relative rotation of the coil spring around its own axis is prevented. The spring seat is engaged with the input and output rotary members while being prevented from rotation around the spring axis.
In this damper mechanism, the coil spring does not rotate around its own axis relatively to the input and output rotary members. Thus, the radially inner and outer portions of the coil spring do not change their positions with each other. Therefore, the timing of the change in the spring constant due to spring compression of each of the coil spring portions does not change, and the intended torsion characteristics can be obtained.
According to a second aspect, the damper mechanism of the first aspect further has a feature such that the radially outer portion of the coil spring has a first space between turns and a second space between turns larger than the first space. Further, the radially inner portion has a third space between turns smaller than the first space and a fourth space between turns larger than the third space. The xe2x80x9cradiallyxe2x80x9d outer and inner portions are the outer and inner portions determined based on a radial direction of the damper mechanism.
According to a third aspect, the damper mechanism of the second aspect further has a feature such that the first and third spaces simultaneously disappear when the coil spring is compressed in accordance with the relative rotation between the input and output rotary members.
According to a fourth aspect, the damper mechanism of the first, second, or third aspect further has a feature such that the number of active turns of the radially inner portion of the coil spring is larger than the number of active turns of the radially outer portion. Since the above state can be maintained, it is possible to prevent a large difference, which may occur in deformation amount per turn between the radially inner and outer portions of the compressed spring. Therefore, it is possible to reduce a difference in stress per turn between the radially inner and outer portions of the compressed spring.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.